DefaultMutableTreeNode root = new DefaultMutableTreeNode ("abc");
DefaultMutableTreeNode node = new DefaultMutableTreeNode ("klm");
root.add (node);
treeModel = new DefaultTreeModel (root);
jTree1.setModel(treeModel);

if (root != null && treeModel != null)
{
   DefaultMutableTreeNode node =
      new DefaultMutableTreeNode ("rst");
   treeModel.insertNodeInto (node, root, 0);
}

    private void jTree1ValueChanged(javax.swing.event.TreeSelectionEvent evt) {
        TreePath p = evt.getPath ();
        Object last = p.getLastPathComponent();
        if (last instanceof DefaultMutableTreeNode)
        {
            DefaultMutableTreeNode node = (DefaultMutableTreeNode) last;
            Object obj = node.getUserObject();
            if (obj instanceof Container && node.getChildCount() == 0)
            {
               Container c = (Container) obj;
 
               for (Component t : c.getComponents())
               {
                   DefaultMutableTreeNode n =
                       new DefaultMutableTreeNode (t);
                   treeModel.insertNodeInto (n, node, node.getChildCount());
               }
            }
        }
 
    }

http://kmlinux/~culik/wiki